I propose to study the genes responsible for formation of the seventy sensory neurons in the free-living nematode Caenorhabditis elegans. I have already identified some twenty chemosensory mutants. I have shown that at least seven of these mutants have morphological alterations in the sensory endings of the nerves in the head. The neuroanatomy of these mutants will be further studied. Since almost all the wild type sensory neuroanatomy is known (Ward, Thomson, White, and Brenner, 1975), it will be possible to determine how the connectivity to the central nervous system is altered in selected mutants. A better selection procedure will be devised to isolate more chemosensory mutants. It is expected that the identification of an attractant produced by bacteria and the use of a preformed gradient of attractant will lead to a more efficient means of selecting additional mutants. Mutants affecting cell position and cell type in the head will be sought by screening clones from mutagenized animals using a light microscope and Nomarski optics or simple histological stains. The isolation of temperature-sensitive and cold-sensitive mutants will enable the time of action and developmental pathway of genes to be determined. The embryogenesis of selected mutants will be studied with the light and electron microscopes. My work will provide a model of the genetic control of development in a simple nervous system.